As polarizers (they are also referred to as polarizing separation elements) used for image display devices such as liquid crystal display devices, projection TVs or front projectors, and showing polarization separation ability in the visible light region, there are absorption polarizers and reflection polarizers.
An absorption polarizer is, for example, a polarizer having a dichroic dye such as iodine aligned in a resin film. However, since such an absorption polarizer absorbs one of polarized light, its light-utilization efficiency is low.
On the other hand, in a reflection polarizer, reflected light not incident into the polarizer is incident again into the polarizer, whereby the light-utilization efficiency can be improved. For this reason, a demand for such a reflection polarizer for the purpose of achieving high intensity of e.g. liquid crystal display devices, is increased.
As a reflection polarizer, there are a linear polarizer constituted by a lamination of birefringent resins, a circular polarizer constituted by a cholesteric liquid crystal and a wire-grid polarizer.
However, such a linear polarizer and a circular polarizer have low polarization separation ability. For this reason, a wire-grid polarizer showing high polarization separation ability is attentioned.
A wire-grid polarizer has a construction comprising a light-transmitting substrate having a plurality of parallel fine metallic wires arranged on the substrate. When the pitch of the fine metallic wires is sufficiently shorter than the wavelength of incident light, in the incident light, a component (i.e. p polarized light) having an electric field vector perpendicular to the fine metallic wires is transmitted, but a component (i.e. s polarized light) having an electric field vector parallel with the fine metallic wires is reflected.
As wire-grid polarizers showing polarization separation ability in visible light region, the following types are known.
(1) A wire grid polarizer comprising a light-transmitting substrate on which fine metallic wires are formed at a predetermined pitch (Patent Document 1).
(2) A wire grid polarizer comprising a light-transmitting substrate having a surface on which a plurality of ridges are formed at a predetermined pitch and a top face and side faces of such a ridge is covered with a film of material of metal or a metal compound to form a fine metal wire (Patent Document 2).
However, the wire grid polarizer of (1) is still insufficient in the polarization separation ability.
The wire grid polarizer of (2) has a higher polarization separation ability than the wire grid polarizer of (1). However, the wire grid polarizer of (2) has a problem that it has a low transmittance in a short wavelength region (in the vicinity of 400 nm).
Further, in the process of producing the wire grid polarizer of (2), a metal is vapor-deposited on the top face of each ridge and a bottom face of each groove between the ridges by a single vapor deposition. However, when a metal is vapor-deposited on the top face of each ridge and on a bottom face of each groove between the ridges by a single vapor deposition, it is not easy to avoid vapor-deposition of the metal on side faces of each ridge. Accordingly, the metal tends to be vapor-deposited on side faces of the ridges, and a fine metallic wire on a top face of a ridge tends to continue to a fine metallic wire on a bottom face of a groove between the ridges. When the fine metallic wire on the top face of a ridge and a fine metallic wire on a bottom face of a groove between the ridges form a continuous film, light cannot be transmitted.